Noise suppression circuits



E. OOSTERHUIS NOISE SUPPRESSION CIRCUITS Oct. '1, 1949.

Filed July 50, 1938 MAIN AEAMPl/F/ER RECEIVER .AUX/L/ARY RECEIVER INVENTOR. E/KgOOSTERh'U/S A TTORNEY.

Patented Oct. 1, 1940 UNETE. STATES rarer NOISE SUPPRESSION CIRUUITS ofDelaware Application July 30, 1938, Serial No. 222,093 In GermanySeptember 21, 193'? 9 Claims This invention relates to a radio-receivingdevice comprising means for suppressing disturbances of short-durationsuch as atmospheric disturbances and disturbances caused by operatingswitches, or by sparks of commutator motors and of the currentcollectors of electrically operated vehicles.

For obviating such disturbances it is known to render a radio-receiverinoperative substan- 10 tially throughout the duration of a disturbance.In this case the disturbance is not reproduced by the loudspeaker andinterruption of the reception is not perceived by the human ear due toits very short duration. For this purpose the receiver may, forinstance, be equipped with a mechanical or electric relay by which thesignal transmitting path is interrupted or short-circuited as soon asthe amplitude of the input voltage of the receiver exceeds a definitethresholdvalue. To ensure that the relay is operated only by thedisturbances and not by the signal to be received the threshold valueshould correspond at least to the maximum amplitude of the signal to bereceived, i. e. with 100% modulation of the signal the thresholdamplitude should be equal to at least double the signal carrier-waveamplitude. Thus, disturbances whose amplitude is smaller than double thecarrier wave amplitude of the signal to be received cannot be avoided bythis arrangement.

In order that disturbances having a smaller amplitude can also besuppressed it has been proposed to control the device, by which thereceiver is rendered inoperative, by means of an auxiliary receivertuned to a wave length which is not used for signals. The auxiliaryreceiver receives only the disturbances so that the threshold value canbe materially reduced. It is presumed for correct operation of such adevice that the disturbances received by the auxiliary receiver are thesame as those received by the principal receiver. Owing to the aperiodiccharacter of the disturbances this requirement is usually met in asatisfactory manner, if the diiference between the signal frequency andthe tuning frequency of the auxiliary receiver be not too large.

The use of an auxiliary receiver for suppressing disturbances ishampered by the fact that at the present state of the broadcast rangethere is hardly a wave length that is not used by some transmitter orother. For this reason the auxiliary receiver must be tuned to afrequency outside the broadcast range, the difference between the signalfrequency and the tuning frequency 55 of the auxiliary receiver beingusually great so that thedisturbances received by the auxiliary receiverno longer correspond to the disturbances occurring in the principalreceiver and freedom from disturbances cannot be ensured in anefficacious manner. 5

According to the invention this drawback is avoided by equipping theauxiliary receiver with a directional antenna. This measure permits theauxiliary receiver to be tuned to a wave length used by a signal, thedirectional antenna being 10 in each instance adjusted so that thesignal in question is not received by the auxiliary receiver. Whenmaking use of the measure according to the invention the auxiliaryreceiver may consequently be tuned to a frequency which only 15 slightlydiffers from the frequency of the signal to be received or evencompletely corresponds thereto, thus ensuring sufficient conformitybetween the disturbances picked up by the auxiliary receiver and theprincipal receiver. 20

The invention will be more clearly understood by reference to theaccompanying drawing representing, by way of example, two forms ofconstruction thereof.

In the arrangement shown in Fig. 1 the oscilla- 25 tions picked up bythe non-directional antenna I are supplied to the principal receiver 2.The low-frequency oscillations occurring after demodulation are, ifdesired after low-frequency amplification, supplied through a couplingcon- 30 denser 3 to the resistance i whose terminals are connectedthrough the intermediary of the relaycontact 5 to the input circuit ofthe final tube 6. The output circuit of the tube 6 comprises the primarywinding of the transformer l to whose 35 secondary winding is connectedthe loudspeaker 8. When receiving a disturbance the relay 9 opens thecontact 5 and thus renders the principal receiver inoperative so thatthe disturbance will not be reproduced by the loudspeaker 8. The coil ofthe relay 9 is connected to the output terminals of an auxiliaryreceiver Hi which is equipped with a directional antenna H. Theauxiliary receiver [0 is preferably furnished with an indicating deviceI2 chosen from known 45 tuning indicators.

After tuning the principal receiver l the auxiliary receiver is tunedwiththe aid of the tuning indicator l2 to a signal whose frequency onlyslightly diliers from the frequency to which the principal receiver istuned. If desired, the auxiliary receiver may be tuned to the samefrequency as the principal receiver to which end the tuning means of thetwo receivers may be coupled together mechanically. After the auxiliaryreceiver has been tuned to a signal the frame antenna II is brought intothe position wherein the tuning indicator indicates a minimum value. Inthis case the signal to which the auxiliary receiver is tuned is nottaken up so that the auxiliary receiver picks up the disturbances only.

Fig. 2 shows an arrangement wherein a separate adjustment of theauxiliary receiver may be dispensed with. In this arrangement theprincipal receiver 2 is also equipped with a frame antenna M which isrigidly connected to the frame antenna H of the auxiliary receiver, thetwo antennae being arranged at right angles to one another. The tuningmeans of the two receivers are mechanically coupled together, as isschematically illustrated by means of the dotted line I5. After theprincipal receiver has been tuned to the desired signal theantenna-system H, I4 is so adjusted that the principal receiver issupplied with a maximum input voltage, which may be easily ascertainedfrom the volume or by means of a tuning indicator. Due to this the frameantenna ii is positioned automatically at right angles to the directionof incidence of the signal to be received, so that the auxiliaryreceiver does not pick up a signal but disturbances. Upon receiving adisturbance the relay 9 inserted in the output circuit of the auxiliaryreceiver closes the contact E3 so that the loudspeaker 8 isshort-circuited and the disturbance is not reproduced.

What is claimed is:

1. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desired carrierfrequency, an arrangement for suppressing disturbances of short durationcomprising an auxiliary receiver, said auxiliary receiver being providedwith a directional antenna and means for tuning the auxiliary receiverto a frequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a minimum of signalenergy, and means responsive to the output of said auxiliary receiverfor impairing the operation of said main, receiver substantiallythroughout the duration of a disturbance.

2. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desired carrierfrequency, an arrangement for suppressing disturbances of short durationcomprising an auxiliary receiver, said auxiliary receiver being providedwith a directional antenna and means for tuning the auxiliary receiverto a frequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a minimum of signalenergy, and means responsive to the output of said auxiliary receiverfor impairing the operation of said main receiver substantiallythroughout the duration of a disturbance, and a common means foradjusting said main and auxiliary receiver tuning means to tune the tworeceivers to said desired carrier frequency.

3. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desired carrierfrequency, an arrangement for suppressing disturbances of short durationcomprising an auxiliary receiver, said auxiliary receiver being providedwith a directional antenna and means for tuning the auxiliary receiverto a frequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a minimum of signalenergy, and means responsive to the output of said auxiliary receiverfor impairing the operation of said main receiver substantiallythroughout the duration of a disturbance, said main receiver collectorbeing a directional antenna adjusted to receive maximum desired signalcarrier energy.

4. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desiredcarrierfrequency, an arrangement for suppressing disturbances of short durationcomprising an auxiliary receiver, said auxiliary receiver being providedwith a directional antenna and means for tuning the auxiliary receiverto a frequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a minimum of signalenergy, and means responsive to the output of said auxiliary receiverfor impairing the operation of said main receiver substantiallythroughout the duration of a disturbance, said main receiver collectorand auxiliary receiver signal antenna being of the loop type andarranged at right angles to one another.

5. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desired carrierfrequency, an arrangement for suppressing disturbances of short durationcomprising an auxiliary receiver, said auxiliary receiver being providedwith a directional antenna and means for tuning the auxiliary receiverto a frequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a of signal energy, andmeans responsive to the output of said auxiliary receiver for impairingthe operation of said main receiver substantially throughout theduration of a disturbance, said main receiver having an audiotransmission network, and said responsive means acting to impair thetransmission through said audio network.

6. In combination with a main radio receiver provided with a signalcollector and means for tuning the receiver to a desired carrierfrequency,

an arrangement for suppressing disturbances of short duration comprisingan auxiliary receiver, said auxiliary receiver being provided with adirectional antenna and means for tuning the auxiliary receiver to afrequency of the order of said desired carrier frequency, saiddirectional antenna being adjusted to pick up a minimum of signalenergy, and means responsive to the output of said auxiliary receiverfor impairing the operation of said main receiver substantiallythroughout the duration of a disturbance, said main receiver collectorand auxiliary receiver antenna being provided by a pair of rigidlyinterconnected frame antennae arranged at right angles to each other.

7. A receiving system comprising a main receiver, means for tuning themain receiver to a desired signal frequency, means for collecting asubstantial amount of signal energy and undesired disturbances, anauxiliary receiver having means for tuning it to said desired frequency,rotatable loop antenna means connected to the auxiliary receiver inputfor collecting a relatively slight amount of signal energy and at leastas much disturbances as said main receiver, and means responsive to theauxiliary receiver output energy for rendering the main receiverinoperative for periods substantially corresponding to the duration ofdisturbances.

8. In combination, a pair of independent receivers, means for tuning thereceivers substantially to a common signal frequency, means forimpressing a maximum magnitude of signal energy accompanied by undesireddisturbances upon one receiver and a relatively small magnitude ofsignal energy accompanied by said disturbances on the second receiver,said impressing means comprising a pair of adjustable signal collectorsarranged in substantially quadrature phase relation, and meansresponsive to the output energy of the second receiver for impairing theoperation of the first receiver for the duration of said disturbances.

9. In combination with a pair of receivers, means for tuning thereceivers over a desired range of signal frequencies, a signal collectorarrangement for the receivers comprising a pair of loop antennaearranged at right angles to each other, each antenna being connected tothe input of an associated one of the receivers, and means responsive tothe output energy of one receiver for impairing the operation of the:other receiver.

EKKO OOS TERI-IUIS.

